It is currently common practice to utilize connector plates of the type having integrally struck teeth to form the joints between the various members comprising a wooden frame. For example, connector plates of various sizes and widths, depending upon the structural requirements of the frames, are commonly embedded in the joints of wooden roof trusses and truss-type floor joists. An example of such connector plates is disclosed in U.S. Pat. No. 2,877,520 of common assignee herewith. To accomplish the foregoing, it is typical industry practice for a frame fabricator to preposition precut wooden members on a jig table in the form of the desired frame and spot precut connector plates on opposite sides of the frame joints. The fabricators then utilize various methods for embedding or pressing the teeth of the connector plates into the opposite sides of the joints to form the completed frame. An example of a fabricating system of this type is illustrated in U.S. Pat. No. 3,602,237 of common assignee herewith. In that patent, precut connector plates are spotted on a jig table on the opposite sides of the joints formed by the prepositioned wooden members, the jig table being then stepped through a press position whereby the joints are successively located between the platens of the press and the connector plates carried thereby embedded into the joints. In U.S. Pat. No. 3,603,244, also of common assignee herewith, the press is moved along the jig table and is automatically stopped at each joint position to embed the connector plates.
Currently, connector plates are provided to frame fabricators in various sizes either cut exactly to the length required or in discrete sizes constituting a multiple of the required lengths. The fabricator cuts these latter longer connector plates to form connector plates of the required lengths. These connector plates, hereinafter sometimes referred to as bar stock, are very often packed by a supplier in one of two ways. The bar stock is either tumble-packed, i.e., the connector plates being randomly disposed in a box, or packed in teeth-to-teeth facing relation. It will be appreciated that teeth-to-teeth packaging requires extensive manual labor to orient the discrete plates in proper position for such packaging. Tumble packing also requires a degree of labor to complete the packaging process and has the additional disadvantage of low density packaging. Furthermore, the fabricator, upon receiving the packages of connector plates, must unpack the plates and individually spot the plates at their proper locations as previously discussed. Where the connector plates are provided in multiples of the desired lengths, the fabricator must, of course, additionally cut these longer connector plates to the desired lengths prior to spotting. Thus, the current practices of handling the plates and securing to a frame requires considerable time and expense.
In the above noted U.S. Pat. No. 3,910,512, there is a described invention wherein manual handling of the connector plates is eliminated and coiled connector plate stock is cut to the required lengths to form connector plates. The machine has a feed assembly which unwinds the coils and advances a leading portion discrete distances toward a press-cut-off assembly, each advance corresponding in distance to the length of the connector plate desired. Two discrete lengths of connector strip are cut from the connector stock and the teeth of the connector plates thus formed are substantially simultaneously embedded into the opposite sides of the joint of prepositioned wooden members.
The described invention of the said patent also includes a conveyor mounting upper and lower press head assemblies on C-frames on opposite sides of the conveyor. Each press head assembly includes a platen, upper and lower platens being located on opposite sides of the frame members on the conveyor and movable toward and away from one another. Clamps carried on the conveyor squeeze wooden chords against the ends of the web framing members. Each press platen carries a cutting blade which cooperates with a fixed cutting blade which cooperates with a fixed cutting surface to cut a selected length of connector plate from the coiled connector stock fed to such press head assembly by the feed assembly. The upper and lower press platens carry the connector plates for embedment into the joint during the final portions of their movement toward one another.
Generally, to complete a frame, the chords and webs are disposed on the conveyor with the chord ends butting the stops carried by the upper press head assemblies and the first web butting the stops carried by the conveyor between the press-cut-off assemblies. Upon acutation, the upper and lower press platens move toward one another cutting predetermined lengths of connector plates from the connector stock. The upper and lower platens carry the plates for embedment into the opposite sides of the joints during the final portions of their strokes. Upon retraction of the platens, the stops for the chords and web are also retracted. In this manner, the partially completed frame comprised of two chords and a first web may be advanced along the conveyor. Particularly, this three-part pallet is advanced by a power roller until the first web butts stops carried by the conveyor spaced a distance from the press heads corresponding to the length of the frame whereby the trailing ends of the chords are located between the press platens. The second web is moved forwardly with the three-part frame until it butts the web stops in line with the press heads whereby the second web is located between the trailing ends of the frame and in a pressing position. As the partially completed frame is advanced and after the first cutting and pressing cycle, the feed mechanism advances the connector stock toward the press head assemblies to locate predetermined lengths thereof between the press platens. Once the trailing web and the chords are positioned between the press head assemblies, the press platens are again actuated to cut connector plates from the stock and embed the teeth thereof into the opposite sides of the joint on opposite sides of the conveyor.
It will be appreciated that significant material handling problems are encountered with respect to connector plates particularly in view of the projecting teeth thereof and that such problems are solved by the described invention in the provision of coiled connector plate stock compatible with a machine which substantially simultaneously cuts the stock and embeds the connector plates thus formed into the joints of a frame. Features of the described machine include the provision of comb-like guides or tines on the fixed cutting blades and in the feed mechanism whereby the machine is virtually jam-proof. The teeth of the connector stock engage in the grooves between the tines and guide surfaces on the opposite sides of the stock from the teeth maintain the stock between the guide surfaces and the edges of the tines. Thus, only longitudinal feeding movement of this stock is permitted with the stock being held against lateral movement by the tines and against movement withdrawing the teeth from between the tines by the guide surfaces. A further novel feature of the described invention resides in the feed mechanism which not only insures that the connector plates are cut to the desired predetermined length but also that the connector stock is cut at a longitudinal location between its teeth. From U.S. Pat. No. 2,877,520, it will be noted that connector plates are provided with teeth arranged in both longitudinal and transversely extending rows. It is important that a transverse row of teeth not be aligned at the juncture of the fixed and movable cutting blades so that the teeth per se are not sheared or weakened by the shearing process. It will be appreciated that connector plates do not have identical tooth-to-tooth spacing in a longitudinal direction. That is to say, an inherent characteristic of a connector plate or stock of this type is that the teeth are spaced from their theoretical longitudinal position progressively further distances in proportion to the length of the stock being fabricated. Accordingly, cumulative error in the longitudinal location of the transverse rows of teeth would result in locating one such row of teeth between the fixed and movable cutting blades. In the machine hereof, however, the connector strip is always cut at a location such that the cutting blades shear through the connector plate per se without engaging any teeth. To accomplish this, a pilot pin is inserted between a pair of transverse rows of teeth prior to each feed to longitudinally adjust the stock relative to the cutting blades to ensure that the teeth are not aligned therewith. The slight error in the location of the teeth relative to one another over the small length of plate between the pin and cutting blades is insignificant and the cut is thereby made substantially medially between next adjacent transversely extending rows of teeth. Thus, the teeth on the opposite sides of the cut remain effective in both the connector plate just formed and the next connector plate to be formed.
A further important feature of the described invention resides in the provision of a fixed cutting blade having a comb-like surface. i.e., tines. The teeth of the connector stock are received between the tines and the ends of the tines support the plate during the shearing operation. The tines thus provide the reaction force for the cutting operation.
A still further important feature of the described invention resides in accurately locating the plate in the joint. It will be appreciated that the plate when cut from the stock tends to first bend away from the movable cutting platen and then jumps from the platen and stock when fully sheared therefrom. To prevent this, the described invention provides a device for holding the plate when it is sheared from the stock. The device includes a dovetail notch or groove carried on the movable cutting blade and a corresponding dovetail projection carried on the fixed blade. When the plate is cut from the stock, a dovetail notch is formed along its trailing edge leaving a dovetail projection on the leading edge of the stock. The dovetail notch on the cut plate engages with the dovetail projection of the fixed cutting blade whereby the plate is held against lateral and longitudinal movement relative to the machine. That is, the plate is held by the dovetail until just prior to embedment of the teeth into the joint. To prevent the forward end of the plate from bending away from the moving platen when cut, a magnet is located on the platen to hold the plate thereagainst. Spring-biased plungers or spring clips may also be utilized on the platens to provide lateral support for the connector plate. These locators ensure that after each plate is cut from the connector stock, it is carried to the joint and located precisely relative thereto.
While the improvements described in that said patent constitute significant advances in the art, that invention also has disadvantages. The coil of connector stock must be wound on a spool in a manner that it can be conveniently unwound and fed to the cutting mechanism of the machine described in the said patent. In practice, therefore, the coil of connector stock is arranged such that either the teeth of the stock are next to the spool or the teeth of the stock project outwardly from the spool.
In the first of these arrangements, the teeth will press into the outer surface of the spool and thus impede removal of the spool from the coil after winding. (This will often also damage the teeth and is not satisfactory, for this reason alone.) This usually requires that each coil be shipped and used with its individual spool. Such arrangement increases the shipping weight of the coil, since the strength of the spool must be rather substantial in order to withstand the winding forces and to subsequently carry and allow unwinding of the coiled connector stock. Further, this arrangement requires a number of the substantial and heavy spools for winding the connector stock, shipping that connector stock to the fabricator and returning used spools for further windings of connector stock. The cost of these spools, of course, increases the overall cost of supplying connector stock to the fabricator, as opposed to the prior methods, noted above, which require no heavy spools or other like apparatus. Indeed, the total cost of shipping these loaded spools to the fabricator and shipping empty spools back to the manufacturer for winding additional connector stock thereon could result in very substantial proportions of the cost of the coiled connector stock.
On the other hand, the connector stock may be wound on the spool so that the teeth project outwardly from the spool and the teeth do not press into the spool so that the spool may be removed from the wound stock, but the finished coil has an outer surface of sharp, projecting teeth which constitutes a hazardous and difficult to handle arrangement. Expensive shipping cases and cartons are therefore required.
Further, according to the method and apparatus discussed above, four spools of connector stock are normally required for full operation of each machine, i.e., two spools to feed the first press head and two spools to feed the second press head. The use of four spools for each machine further complicates the operation of the machines.
As can be appreciated, therefore, it would be of significant advantage to the art if the arrangement of the coils of connector stock could be retained while avoiding the disadvantages noted above. Avoiding these disadvantages would result in substantial savings in shipping cubes and provide significant increased ease in handling the coil connector stock.